Which one of the following statement is not true ?

Options

A. Oxides of sulphur, nitrogen and carbon are the most widespread air pollutant
B. pH of drinking water should be between 5.5 - 9.5
C. Concentration of DO below 6 ppm is good for the growth of fish
D. Clean water would have a BOD value of less than 5 ppm

Answer

To determine which statement is not true, we will analyze each of the provided statements one by one.

### Step 1: Analyze the first statement
**Statement:** "Oxides of sulphur, nitrogen, carbon are widely spread and air pollutants."

- **Analysis:**
- Oxides of sulfur (SOx), nitrogen (NOx), and carbon (CO) are indeed recognized as significant air pollutants. They are commonly found in the atmosphere due to industrial activities, vehicle emissions, and other sources.
- Conclusion: This statement is true.

### Step 2: Analyze the second statement
**Statement:** "The pH of drinking water should be between the value of 5.5 to 9.5."

- **Analysis:**
- The ideal pH range for drinking water is typically between 6.5 to 8.5. A pH below 5.5 is considered too acidic, and a pH above 9.5 is too alkaline for safe drinking water.
- Conclusion: This statement is not true.

### Step 3: Analyze the third statement
**Statement:** "Concentration of DO (dissolved oxygen) below 6 ppm is good for the growth of fishes."

- **Analysis:**
- Fish typically require a dissolved oxygen level of at least 4 ppm for healthy growth, with some species needing higher levels. A level of 6 ppm is acceptable for many fish species, but it is not harmful.
- Conclusion: This statement is true.

### Step 4: Analyze the fourth statement
**Statement:** "Clean water should have a BOD (Biochemical Oxygen Demand) of less than 5 ppm."

- **Analysis:**
- Clean water is generally expected to have a BOD of less than 5 ppm, often around 4 to 5 ppm. This indicates a low level of organic pollutants.
- Conclusion: This statement is true.

### Summary of Findings
- The first statement is true.
- The second statement is not true (this is the answer we are looking for).
- The third statement is true.
- The fourth statement is true.

### Final Answer
The statement that is not true is: **"The pH of drinking water should be between the value of 5.5 to 9.5."**

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